Clues supporting photoperiod as the main determinant of seasonal variation in amphibian activity

Abstract

Organism survival and reproduction are affected by the ability to synchronize behaviour and physiological condition to the season, typically using photoperiod. However, temperature and rainfall have been repeatedly invoked as determinants of annual reproductive cycles in amphibians. This putative role of environmental conditions determining amphibians' activity was recently challenged in favour of photoperiod or a combination of environmental variables as more plausible clues. We evaluated the alternative variables potentially used by amphibians to track season fluctuations. The seasonality of a system was captured in a structural equation model, which identified photoperiod as the variable that represents seasonal variations in amphibian richness and climatic conditions. Congruently, reconstruction of amphibian seasonality with a sinusoidal model captured the same information as a linear regression between richness and photoperiod. Available evidence suggests that amphibians could be tracking photoperiod, over temperature and rainfall, as the proximate factor determining their seasonal variation in physiology and activity.

Keywords:

• photoperiod
• Anura
• seasonality
• assemblages
• structural equation model
• latent variables

Acknowledgements

We thank A. Camargo, I. da Rosa, R. Maneyro, and D. E. Naya for help on fieldwork and comments on data interpretation, M. Root-Bernstein and A. Camargo for contributions on English editing. This article was fund by a grant of Programa de Desarrollo de las Ciencias Básicas (PEDECIBA, Uruguay) to AC. MA is grateful for the support of Progama de Desarrollo Tecnológico (PDT 71-10) and FONDECYT-FONDAP grant 1501-0001 (Programs 2). We are very grateful to three anonymous reviewers for their comments on an earlier version of this manuscript. AC is very grateful to E. Castiñeira without her support this work would not have been possible.